Extractive oxidation used as a naphtha treating process is well-known, for example, the sweetening naphtha process, typically comprising a catalytic oxidation via O2 in the presence of NaOH or KOH of odor-generating mercaptans of certain raw naphthas, more specifically those from fluid catalytic cracking. See U.S. Pat. No. 2,591,946 where is taught a sweetening process for sour oils whereby mercaptans are removed from said oils by carrying out a reaction the catalyst of which is KOH, O2 and 0.004 to 0.1 wt % copper oxide based on the KOH solution.
Also, an article in the Oil and Gas Journal vol. 57 (44) p. 73–78 (1959) entitled “Low Cost Way to Treat High-Mercaptan Gasoline” by K. M. Brown et al, is directed to the discussion of the Merox process and other prior art procedures.
However, such process does not apply to raw naphthas where the target substances are those containing unsaturation and nitrogen functionalities, mainly those nitrogen functionalities of a basic character, which cause not only odor but also naphtha instabilities due to color as well as turbidity caused by gums, not to mention that those basic nitrogen substances are harmful to the hydrodesulfurization treatment processes used as naphtha finishing processes before commercialization.
The peroxide-aided oxidation is a promising path for the refining of fossil oils, and may be directed to several goals, for example to the removal of sulfur and nitrogen compounds present in fossil hydrocarbon streams, mainly those used as fuels for which the international specification as for the sulfur content becomes more and more stringent.
One further application is the withdrawal of said compounds from streams used in processes such as hydrotreatment, where the catalyst may be deactivated by the high contents in nitrogen compounds.
Basically, the peroxide oxidation converts the sulfur and nitrogen impurities into higher polarity compounds, those having a higher affinity for polar solvents relatively immiscible with the hydrocarbons contaminated by the sulfur and nitrogen compounds. This way, the treatment itself comprises an oxidation reaction step followed by a separation step of the oxidized products by polar solvent extraction and/or adsorption and/or distillation.
The oxidation reaction step using peroxides, as well as the separation steps of the oxidized compounds from the hydrocarbons have been the object of various researches.
Thus, EP 0565324A1 teaches a technique exclusively focused on the withdrawal of organic sulfur from petroleum, shale oil or coal having an oxidation reaction step with an oxidizing agent like H2O2 initially at 30° C. and then heated at 50° C. in the presence of an organic acid (for example HCOOH or AcOH) dispensing with catalysts, followed by (a) a solvent extraction step, such as N,N′-dimethylformamide, dimethylsulfoxide, N,N′-dimethylacetamide, N-methylpyrrolidone, acetonitrile, trialkylphosphates, methyl alcohol, nitromethane among others; or by (b) an adsorption step with alumina or silica gel, or (c) a distillation step where the improved separation yields are caused by the increase in boiling point of the sulfur oxidized compounds.
A similar treatment concept is used by D. Chapados et al in “Desulfurization by Selective Oxidation and Extraction of Sulfur-Containing Compounds to Economically Achieve Ultra-Low Proposed Diesel Fuel Sulfur Requirements”, NPRA 2000 Annual Meeting, Mar. 26–28, 2000, San Antonio, Tex., Paper AM-00-25 directed to a refining process also focused on the reduction of the sulfur content in oils, the oxidation step occurring at temperatures below 100° C. and atmospheric pressures, followed by a polar solvent extraction step and by an adsorption step. The authors further suggest the use of a solvent recovery unit and another one for the biological treatment of the concentrate (extracted oxidized products) from the solvent recovery unit, this unit converting said extracted oxidized products into hydrocarbons.
According to the cited reference by Chapados et al., the reaction phase consists of an oxidation where a polarized —O—OH moiety of a peracid intermediate formed from the reaction of hydrogen peroxide and an organic acid performs an electrophilic oxidation of the sulfur compounds, basically sulfides such as benzothiophenes and dibenzothiophenes and their alkyl-related compounds so as to produce sulfoxides and sulfones.
U.S. Pat. No. 3,847,800 teaches that the oxidation of the nitrogen compounds, such as the quinolines and their alkyl-related compounds so as to produce N-oxides (or nitrones) can be promoted as well when reacting these compounds with a nitrogen oxide.
The mechanisms for the oxidation of sulfur containing compounds with a peracid derived from a peroxide/organic acid couple are shown in FIG. 1 attached, with dibenzothiophene taken as model compound.
According to U.S. Pat. No. 2,804,473, the oxidation of amines with an organic peracid leads to N-oxides, therefore a reaction pathway analogous to that of sulfur-containing compound is expected for the oxidation of nitrogen-containing compounds with a peracid derived from the peroxide/organic acid couple, as shown in FIG. 2 attached, with quinoline taken as model compound. In addition, the same US patent teaches a process for the production of lower aliphatic peracids. According to this publication, peracids are useful in a variety of reactions, such as oxidation of unsaturated compounds to the corresponding alkylene oxide derivatives or epoxy compounds.
As illustrated in FIG. 3 attached, it is also well-known that hydrogen peroxide naturally decomposes into unstable intermediates that yield O2 and H2O, such process being accelerated by the action of light, heat and mainly by the pH of the medium.
U.S. Pat. No. 5,917,049 teaches a process for preparing dicarboxylic acids containing at least one nitrogen atom where the corresponding heterocyclic compound of fused benzene ring bearing at least one nitrogen atom is oxidized in the presence of hydrogen peroxide, a Bronsted acid and an iron compound. The preferred iron compound is iron nitrate and nitric acid is used as the Bronsted acid. The reaction occurs in an aqueous medium.
Besides, U.S. Pat. No. 4,311,680 teaches a process for removal of sulfur containing compounds such as H2S, mercaptans and disulfides from gas streams exclusively such as natural gas by flowing the said gas stream through a Fe2O3 fixed bed in presence of an aqueous solution of hydrogen peroxide.
On the other hand, several publications report the use of the Fenton's reagent exclusively directed for the withdrawal of pollutants from aqueous municipal and industrial effluents. See the article by C. Walling, “Fenton's Reagent Revisited”, Accts. Chem. Res., Vol. 8, p. 125–131 (1975), U.S. Pat. No. 6,126,838 and U.S. Pat. No. 6,140,294 among others.
Fenton's reagent, known since 1894, is traditionally a mixture of H2O2 and ferrous ions exclusively in an aqueous medium, so as to generate the hydroxyl radical OH as illustrated in FIG. 4 attached. The hydroxyl radical is one of the most reactive species known. Its Relative Oxidation Power (ROP) ROP=2.06 (relative to Cl2 whose ROP=1.0), is higher than that for example of singlet oxygen (ROP=1.78)>H2O2(ROP=1.31)>HOO(ROP=1.25)>permanganate(ROP=1.24), this making it able to react with countless compounds.
However, side reactions consume or compete with the hydroxyl radical due to the presence of Fe3+ or due to the natural dissociation of the hydrogen peroxide, as illustrated in FIG. 5 attached.
Such side reactions may be minimized by reducing the pH in the medium, since the protic acidity reverts the dissociation equilibrium of the H2O2 into H+ and OOH− (as per FIG. 3 attached), so as to prevent the transformation of the generated OOH— into HOO which will lead more H2O2 to H2O and O2 in spite of the co-generation of the desired hydroxyl radical. On the other hand, excessive lowering of pH leads to the precipitation of Fe(OH)3 that catalyses the decomposition of H2O2 to O2.
Thus, it is recommended to work at pH 2.0–6.0, while afterwards adjusting the reaction pH until 6.1–9.0 to allow for a better separation of the products by flocculation of the residual ferrous sulfate salts, when this salt is the source of ferrous cations of the conventional Fenton's reagent.
However, in case of any free ferric cations are produced and consume or inhibit the generation of the hydroxyl radical (as per FIG. 5), those could be scavenged by complexing agents (as for example phosphates, carbonates, EDTA, formaldehyde, citric acid) only if those agents would not at the same time scavenge the ferrous cations also solved in aqueous media and required for the oxidation reaction.
Sources of active Fe attached to a solid matrix known as useful for generating hydroxyl radicals are the crystals of iron oxyhydrates FeOOH such as Goethite, used for the oxidation of hexachlorobenzene found as a pollutant of soil water resources.
R. L. Valentine and H. C. A. Wang, in “Iron oxide Surface Catalyzed Oxidation of Quinoline by Hydrogen Peroxide”, Journal of Environmental Engineering, 124(1), 31–38 (1998), relate a procedure to be used exclusively on aqueous effluents using aqueous suspensions of ferrous oxides such as ferrihydrite, a semicrystalline iron oxide and goethite, both being previously synthesized, to catalyze the hydrogen peroxide oxidation of a model water polluting agent, quinoline, present in concentrations of nearly 10 mg/liter in an aqueous solution the characteristics of which mime a natural water environment. Among the iron oxides used by the authors, a suspension of crystalline goethite containing a complexing agent (for example carbonates) produced higher quinoline abatement from the aqueous solution, after 41 hours reaction. According to the author, the complexing agent is adsorbed on the catalyst surface so as to regulate the decomposition of H2O2. The article does not mention the formed products and the Goethite employed was a pure crystalline material synthesized by aging Fe(OH)3 at 70° C. and pH=12 during 60 h.
Pure goethite such as the one utilized by Valentine et al. is hardly found in free occurrences in the nature; however, it can exist as a component of certain natural ores.
U.S. Pat. No. 5,755,977 teaches a process where a contaminated fluid such as water or a gas stream containing at least one contaminant is contacted in a continuous process with a particulate goethite catalyst in a reactor in the presence of hydrogen peroxide or ozone or both to decompose the organic contaminants. It is mentioned that the particulate goethite may also be used as a natural ore form. However, the particulate goethite material actually used by the author in the Examples was a purified form purchased from commercial sources, and not the raw natural ore.
Goethite is found in nature in the so-called limonite and/or saprolite mineral clays, occurring in laterites (natural occurrences which were subjected to non-eroded weathering, i.e. by rain), such as in lateritic nickel deposits, especially those layers close by the ones enriched in nickel ores (from 5 to 10 m from the surface). Such clays constitute the so-called limonite zone (or simply limonite), where the strong natural dissolution of Si and Mg leads to high Al, Ni concentrations (0.8–1.5 weight %), also Cr and mainly Fe (40–60 weight %) as the hydrated form of FeOOH, that is, FeOOH.nH2O.
The layers below the limonite zone show larger amounts of lateritic nickel and lower amounts of iron as Goethite crystals. This is the so-called saprolite zone or serpentine transition zone (25–40 weight % Fe and 1.5–1.8 weight % Ni), immediately followed by the garnierite zone (10–25 weight % Fe and 1.8–3.5 weight % Ni) that is the main source of garnierite, a raw nickel ore for industrial use.
The open literature further teaches that the crystalline iron oxyhydroxide FeOOH may assume several crystallization patterns that may be obtained as pure crystals by synthetic processes. Such patterns are: α-FeOOH (Goethite cited above), γ-FeOOH (Lepidocrocite), β-FeOOH (Akaganeite), or still δ′-FeOOH (Ferroxyhite), this latter having also magnetic properties. The most common crystallization patterns are Goethite and Lepidocrocite.
The iron oxyhydroxide crystalline form predominant in limonite is α-FeOOH, known as Goethite. The Goethite (α-FeOOH) crystallizes in non-connected layers, those being made up of a set of double polymeric ordered chains. This is different, for example, from the synthetic form Lepidocrocite (γ-FeOOH), which shows the same double ordered chain set with interconnected chains. This structural difference renders the α-FeOOH more prone to cause migration of free species among the non-connected layers.
Limonite contains iron at 40–60 weight % besides lower contents of nickel, chrome, cobalt, calcium magnesium, aluminum and silicon oxides, depending on the site of occurrence.
The specific area of limonite is 40–50 m2/g, besides being a low cost mineral, of easy pulverization and handling; its dispersion characteristics in hydrophobic mixtures of fossil hydrocarbons are excellent.
Limonite was found to be easily dispersed in fossil oils as a precursor of pyrrothite (Fe1−xS), as reported by T. Kaneko et al in “Transformation of Iron Catalyst to the Active Phase in Coal Liquefaction”, Energy and Fuels 1998, 12, 897–904 and T. Okui et al, in “Proceedings of the Intl. Symposium on the Utilization of Super-Heavy Hydrocarbon Resources (AIST-NEDO)”, Tokyo, Sept. 2000.
This behavior is different from that of a Fe(II) salt such as ferrous sulfate or ferrous nitrate, that requires an aqueous medium to effect the formation of Fenton's reagent.
Thus, the present invention makes use of the oil dispersion character of pulverized limonite ore in order to perform the direct Fenton-type oxidation of sulfur, nitrogen, conjugated dienes and other unsaturated compounds present in naphtha streams, in addition to the classical oxidation worked by peracids alone.
U.S. Ser. No. 09/855,947 of May 15, 2001 of the Applicant and fully incorporated herein as reference, teaches the catalytic oxidation of organic compounds in a hydrophobic, fossil oil medium in the presence of a peracid (or peroxide/acid couple), the oxidation reaction being catalyzed by an iron oxide such as a pulverized limonite ore working as a highly-dispersible source of catalytically active iron in this oil medium.
Thus, the literature mentions processes for the treatment of organic compounds from fossil oils through oxidation in the presence of peracids (or peroxides and organic acids), as well as treating processes of aqueous or gaseous media using the Fenton's reagent. U.S. Ser. No. 09/855,947 of May 15, 2001 is directed to the catalytic oxidation of organic compounds in a hydrophobic, fossil oil medium in the presence of a peracid (or peroxide/acid couple), the oxidation reaction being catalyzed by an iron oxide such as a pulverized limonite ore working as a highly dispersible source of catalytically active iron in this oil medium. However, there is no description nor suggestion in the literature of an extractive oxidation of heteroatomic polar compounds, conjugated dienes and other unsaturated moieties from raw hydrocarbon streams, whereby such compounds are oxidized in the presence of an aqueous slurry of a peroxide solution/organic acid couple and an iron oxide ore and simultaneously removed from said streams by the oxidant itself, said process being described and claimed in the present invention.